Scott Swartz's AD-3208 Analog Delay is Awesome!

[Jason M.]

Finally finished Scott's analog delay and it worked first time I fired it up.

Sounds great! Really nice and warm sounding repeats. Does the self oscillation noise thing too.

I first tried it without the delay chips in to make sure I got dry signal through it. The trimpots were all set to their midpoint after the delay chips were installed (I used two MN3205 chips for max. delay time). At first, the delay came though but was distorted, so I tweaked the bias trimpots by ear to clean up the delay (too impatient to calibrate with the scope right now).

I started building pedals five years ago with the ultimate goal to build an analog delay pedal. The only pcb layouts I found were geared toward rack mount units and used impossible to find BBDs (SAD4096). Thanks to Scott Swartz for sharing such a great design! And to JD Sleep at General Guitar Gadgets for a perfect PCB.

Has anyone else built this?

[JT]

I built the PT80 which i absolutely love i would be interested in a comparison between the two .anyone build both?

[KlausSp]

Hi!

Can you tell me where to get a schematic for the delay?

Greetings,

Klaus

[smallbearelec]

Klaus--

The schem and layout are at www.generalguitargadgets.com. To anticipate a question: I do have left a few dozen of the MN3205 that Jason mentioned, and large stock of the BL3208B.

Regards
Steve Daniels
www.smallbearelec.com

[fretbuzz2003]

Jason,
I just ordered the parts last night to build the analog delay. What size enclosure did you use? I ordered the Eddystone "C" size box, hoping I'd be able to mount the PCB above the pots and squeeze everything else in, but now I'm having second thoughts.

[Ed G.]

I built the PT80 which i absolutely love i would be interested in a comparison between the two .anyone build both?

Scott's notes indicate that they sound very similar but the PT-80 has longer delay times.
I've only built the PT80 and I love it as well. It is not overbearing as a digital delay usually sounds, very smooth and atmospheric. I can see myself getting addicted to it and using it a lot.

[Jason M.]

Jason,
I just ordered the parts last night to build the analog delay. What size enclosure did you use? I ordered the Eddystone "C" size box, hoping I'd be able to mount the PCB above the pots and squeeze everything else in, but now I'm having second thoughts.

I also used the "C" size enclosure and everything fit nicely. It could probably be shoehorned into a 1590BB size (look at the pics of the PT-80 at the general guitar gadgets website), but I scavenged an enclosure that was already drilled from a failed project.

There are a few tight traces that I had to fix solder bridges on, so watch out for that. But then again, I'm pretty sloppy.

I never could get the onboard millenium-type bypass to work, so I am just going to use a 3PDT.

Good luck!
J.

[Ed G.]

In regards to the milennium bypass, what kind of LED are you using? I used an ultrabright blue and it works perfectly with the J201 fet as per Scott's notes.

[Jason M.]

In regards to the milennium bypass, what kind of LED are you using? I used an ultrabright blue and it works perfectly with the J201 fet as per Scott's notes.

I used a 2N5457 with a superbright amber LED. The LED stays on all the time and pops when switched in OR out.
I will try a J201.

[Mark Hammer]

Note to Scott,

I wonder if it would be possible to draft a board layout to use a single 3207 for a simple slapback echo?  Everything else seems set up for it.  All that is different is the use of one 3207 instead of two 3208's.  Different pinouts, of course, but the other aspects (clock, bias, etc.) are the same.

[Scott Swartz]

Lots of questions, and here are my thoughts.

On boxing it, I did not mention it in the documentation, but my concept was to use the 1590C box in a "2 layer arrangement", ie pots, jacks, etc on the lower level and the PCB on 1.25 long standoffs occupying the higher level.  I have all the parts, but haven't assembled it yet.  So fretbuzz2003 and Jason M. reached the same conclusion as far as what is workable.  I did look at the 1590BB and I think that it will be REALLY tight, maybe its possible. If the 3.3 long dim was 3.1, it would definitely work, but I wasn't able to squash the board down to that and keep the big areas for the poly coupling caps.  If it were redesigned to use electros and stand up resistors it could be done I guess.  Another option would be make the PCB bigger and have pads for the footswitch on the board ala Voodoo Labs, but then its less general and the exact footswitch would have to be used.

The millenium circuit should work fine the trace layout is correct, could be bad parts, and the millenium is best with a super bright LED that doesn't need 10 ma like a normal one does.  One refinement is the extra diode in the series connection of LED/resistor/diode that connects to the source of the FET.  This in conjunction with the bleed resistor kills the millenium dim glow issue 100%, and also makes the FET choice less critical, I could never get the dim glow with any of a handful of different model FETs I tried.

A single 3208 would work for slapback, would it not?  For use with a single BBD, it would be a simple matter to leave off the parts for the second BBD and just use a jumper from the wiper of the 1st BBD balance pot (input side of the 1 uF cap feeding to the 2nd BBD), to the input of the post delay filter (wiper of removed 2nd BBD balance pot). Since the BL3208 is so cheap, this approach might be the best.  The pinout of the 3207 is scrambled as compared to the 3208/3205, it would require some re routing of traces rather than just moving pads.

[Ed G.]

I wasn't able to squash the board down to that and keep the big areas for the poly coupling caps.  If it were redesigned to use electros and stand up resistors it could be done I guess.  

Scott, I built the PT-80 and ordered 1 uf poly caps from Steve at Small Bear. They came in and they were these little blue box-type caps, I had to be very careful to bend the leads because they were spaced pretty narrow and the lead length was short, just enough to where I could get it through the PCB and have enough lead to solder it.
If you check out these caps and design a PCB around them, I believe you could substantially reduce the size of the PCB. They don't make a footprint much larger than an electrolytic cap. Steve at Small Bear should have the dimensions on these caps.